The invention relates to gear drives and clutch systems therefor and in particular a clutch to prevent damage to a gear drive when one gear jams.
In gear drives, such as those usd in vertical blinds, a driving gear is rotated to rotate a driven gear. The driven gear is on the end of a shaft which positions the tilt of the slats of the blind. When the slats reach their most extreme tilt position in either direction, the shaft and the driven gear are stopped. At this point the operator will still be activating the driving gear, usually by a pull chain wrapped partially around the driving gear. If the operator continues to pull on the chain after the driven gear has stopped, damage may occur to the teeth of the driving gear and/or the driven gear.
It is known to protect a gear drive by use of an override coupling. For example, in a vertical blind each of the slat carriers may have a ratcheted connection to the tilt shaft so that when the salts jam or reach an extreme position the tilt shaft spins without jamming. Also, it is known to key the driven gear to its shaft with a key that will shear prior to the system obtaining a stress level which would damage the gears. In the first situation, no protection is afforded the gear drive if the shaft jams due to forces not applied to the slats. Furthermore, a failure in the ratchet of any one carriage's ratchet could damage the entire system. In the keyed type structure, the key must be replaced after each successful operation of the clutch.